Piston ring grinding machine



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PISTON RING GRINDING MACHINE Filed June 15, 1938 9 Sheets-Sheet 1 JuIy30, 1940. R. w. YOUNG 2,209,711

PISTON RING GRINDING MACHINE Filed June 15, 1938' 9 Sheets-Sheet 2 J2 *g a aflo gow y July 30, 1940. v R, w YQUNG 2209,71]

' rzswon RING GRINDING momma Filed June 15. 1938- I 9 Sheizs-Sheet :s

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PISTON RING GRINDING MACHINE Fired June 1938 9 Sheets-Sheet. 4.

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4 PISTON RING GRINDING MACI -IINE Filed June 15, 1938 9 Sheets-Sheet 5 July 30, 1940- R. w. YOUNG PISTON RING GRINDING MACHINE Filed June 15, 1938 9 Sheets-Sheet 6 Fl IF N% 9% QM. Ev

R. W. YOUNG PISTON RING GRINDING MACHINE July 30, 1940.

Filed June 15, 1958 9 Sheet-Sheet 7 .wh Oh zig Q 8 NH Q NH Qmv OMV wn July 30, 1940. I w YQUNG I 2,209,711

PISTON RING GRINDING MACHINE Filed June 15; 1938 9 Sheets-Sheet 8 July30, 1940. YOUNG 2,209,711

PISTON RING GRINDING MACHINE Filed June 15, 1938 9 Sheets Sheet 9 INTERMITTENT )ONTINUOUS ,5 g 3 jwewzzfo/ Patented July 30, 1940 PATENT OFFICE 2,209,711 7 PISTON RING GRINDING MACHINE Ralph Waldo Young, Beloit, Wis., assignor to Charles H. Besly & Company, Chicago, 111., a

corporation of Illinois Application June 15, 1938, Serial No. 213,767 3 Claims. ((151-112 This invention relates to improvements in double spindle grinding machines ofithe type particularly adapted for finishing the top and bottom surfaces of piston rings and similar flat pieces, although not necessarily limited to such use.

Among the objects of the invention is to pro- .vide a machine of the character described where- I in piston rings are continuously fed between the two opposed grinding wheels and ground or finished to a predetermined uniform thickness within exceptional limits of precision.

A further object of the invention is to provide improved meansfor feeding the grinding wheels toward each other to compensate for wear, together with means for automatically dressing the grinding surfaces so as to maintain the wheels in proper working relation ,with eachother as well as to maintain their grinding surfaces in proper cuttingcondition.

Other features and objects of the invention will appear from time to time'as the following description proceeds.

The invention may best be understood by reference to the accompanying drawings, in which Fig. 1 is a front view of a machine constructed in accordance with'my invention,. and with the grinding wheel hoods removed.

Fig. 2 is a side view of the machine shown in Fig. 3 is a plan view of the machine.

Fig. 4 is an enlarged side view of the machine, but with parts omitted'to show the general arrangement of the two grinding wheels and themeans for feeding them toward each'other to 35 compensate for wear.

Fig. 5 is an enlarged detail section taken generally on line 5-5 of Fig. 2, and showing portions of the compensating feed mechanism and the dress-' ing mechanism for the upper wheel.

Fig. 6 is an enlarged detail section of the compensating feed clutch and index wheel.

-' Fig. 7 is an enlarged detail section taken generally along the piston ring feed guideway, and showing the grinding wheels in side elevation. V

Fig. 8 is a detail section taken generally on line 88 of Fig. '7.

Fig. 9 is a view somewhat similar to Fig. 8, but drawn to a somewhat larger scale and with parts of the piston ring guide supports broken away to show the feed guideway in greater detail.

Fig. 10 is a detail section taken longitudinally of the piston ring feed guideway shown in Fig. 9, and showing the grinding wheels in section.

5 Fig. 11 is an enlarged detail view of the front dresser point. 1

platen for supporting the'rings as they enter the grinding zone.

Fig. '12 is an enlargeddetail section taken on line 12 |2 of Fig. 10.

Fig. 13 is a horizontal detail section taken gen- 5 erally on line I3l 3 of Fig. 1, with parts removed to show details of the wheel dressing mechanism.

Fig. 14 is a perspective detail view of one of the dressing tools and adjustable gauge stool for the 10 Fig. 15 is a wiring diagram of the electrical connections for controlling the operation of the dressing mechanism.

Referring now to details of the embodiment of my invention illustrated in the drawings, the 'mal5 chine shown therein includes a base It having a main supporting column ll rigidly mounted thereon. A pair of similar grinding wheel assemblies indicated'generally at A and B are mounted on vertical saddles l2 and I3 at one side of said column, with their respective grinding wheels N and I5 arranged in opposed lapping relation to each other, but with their vertical axes offset laterally. Said grinding wheels have annular grinding discs or surfaces I l and IF, respectively, arranged so that their inner edges are tangential with the outer edge of the other annular surface at the point of maximum overlap, as is best seen in Figs. ,3, 4 and 9,3 The central portion of said supporting columfi'i' between said saddles l2 and 80 I3 is recessed at I 1 to accommodate the grinding wheels.

The two wheel assemblies A and Bare substantially identipal with each other; including the means for feeding their respective wheels axially toward each other so as to compensate for wear -on their grinding surfaces.

mounted therein as by ball bearings 25 and 26. v

The upper end of the spindle 24 has a splined connection at 21 with a drive pulley 28 which is. rotatably supported at the upper end of the casing 20. The wear-compensating mechanismfor feeding the wheel l4, spindle 2t and its bearing support 23 in a downward direction includes an electric motor 30 which operates through a mu1tl-' q;

ple gear reduction mechanism of any well known form, as indicated generally at 3 I, to drive a bevel pinion 32 meshed with bevel pinion 33 on a threaded stud 35 which passes upwardly through a sleeve 34 fixed on the casing 20 adjacent one side of the bearing support 23. The upper end of stud 35 engages a projecting lug 36 integral with the bearing support 23. With this arrangement it will be seen that the weight of the wheel I4 and its'bearing support normally rests upon the upper end of the threaded stud 35 and as said stud is gradually backed away by operation of the motor 30 through its geared connections, the

wheel is fed downwardly at a slow rate, sufiicient to compensate for wear on its grinding surface.

Means are provided for counterbalancing the weight of the wheel and its bearing support 23, which herein consists of a counterweight 31 (see Figs. '1 and 3) located at one side of the column II and connected by cable 38 over pulley '39 and segment 40 to a shaft 4| passing through one side of the casing 20, and having a pinion 42 engaging a rack 43 fixed on one side of the bearing support 23. A hand lever 45 is also connected to the outer end of the shaft to permit manual elevation of the wheel when desired, as for instance during adjustments of the machine.

The speed of automatic feed can be regulated mechanically in any desired manner. In the form shown herein, the drive motor 38 is connected' to the gear reduction mechanism 3| by adjustable belt and pulley drive of the Reeves type, affording variations in the feeding speed as desired.

Means are also provided for disconnecting the gear drive to the bevel pinion 32 at will, and operating said bevel pinion by hand for quick vertical adjustment. Details of this mechanism are shown in Fig. .6 in which the shaft 32 carrying bevel pinion 32 is normally driven from a helical gear 3 I forming part of the gear reduction mechanism 3I. Said helical gear 3 I is loosely mounted on the shaft 32 and is adapted to be engaged by a clutch member I6 splined on shaft-32 and movable intoand out of frictional engagement with gear 3| by means of a hand wheel I1. When the clutch is disengaged, the pinion shaft 32 is free to be rotated by means of a handle 46.

An indexing wheel I8 is also fixed on the clutch member I6 and has a pointer IIl associated therewith to indicate the vertical position of adjustment of the spindle 24.

The lower wheel assembly B is substantially the same in construction as the upper assembly just described, excepting that in the case of the lower assembly, of course, the wheel is fed up-- wardly against gravity. Accordingly, in the case ofthe lower wheel assembly a counterbalancing weight 31 is provided, which is considerably heavier than the corresponding counterweight 31 of the upper wheel assembly so as to urge the wheel I5 upwardly against gravity. The counterweight 31 is connected through cable 38 and segment 40 to shaft 4|. As in the case of the upper wheel, the shaft 4 I of the lower wheel assembly has a pinion 42 engaging rack 43 and tending to elevate the lower wheel I5 upwardly under control of its threaded stud 35.

The grinding wheels I4 and I5 are continuously rotated by any suitable drive means, as for instance, by electric motors suitably mounted within hollow upper and lower portions of the column II and connected by belts to the drive pulleys 28 on their respective drive spindles 24.

Referring now to the construction and ar- .laterally from the main column II.

rangement for guiding the piston rings through the machine, special reference may be had to Figs. 7 to 12, both inclusive.

The piston rings 41 are fed laterally from the bottom of a magazine 48 mounted on a standard 48' at the front-0f the machine. The feeding means herein shown, consists of a plurality of rubber rollers 49, 49 all rotating in the same direction to progress the rings successively from the bottom of the magazine beneath an upper idler roller 49 into a horizontal feeding guideway indicated generally at 50. The feed rollers 49 are driven by a motor 5| through suitable gear reduction mechanism including pulleys 52, 53, belt 54 and a multiple shaft drive gearing of well known form-indicated generally at 55, details of which need not be described herein as the ring feeding mechanism forms no part of the present invention.

The piston ring guideway 50 is formed in part by a pair of parallel side bars 56 passing through the machine between the upper and lower grind wheels I4 and I5, and spaced on opposite sides of the common diameter including the axes of the two grinding wheels, as is clearly seen in Figs. '7 and 8. As shown herein, said side bars 56 consist of strips of sheet metal, anchored'at one end adjacent the magazine 48 at the front of the machine, and at the opposite end to a rocking member 51 pivotally mounted on a bracket 58 projecting from the main column II at the rear of the machine. The two side bars 56 are maintained under tension by means of adjustable bolts 59 which control the tilted position of the rocking member 51, as clearly shown in Fig. '7.

The bottom of the guideway 50 between the grinding wheel I5 is formed by a platen 68 fixed with its upper face in substantially the same plane as that of the said grinding wheel. From platen 60 the rings are passed over the exposed outer periphery of the lower wheel disc and from thence across two platens 6I and 62. The latter platens are supported in fixed position within the recessed central portion 63 of the lower wheel by 1 means of an overhanging bracket 64 extending As shown in Figs. 8 and 9, a bed plate ,65 is rigidly suspended from the bracket 64 within the central recess 63 by vertical rods 66, 66 depending on opposite sides of the side bars 56. The two platens 6| and 62 are adjustably mounted on bed plate 65 by means of countersunk screws 61, preferably three in number, and each passing through a rubber washer 68 interposed between the bottom of the platen and the bed plate 65 (see also Fig. 10) With this arrangement, the upper surfaces of the two platens are capable of veryclose adjustment both vertically and planarly, relative to the surfaces of the adjacent grinding wheels so as to control the position of the rings as they are introduced into the grinding zone, as will hereinafter more fully appear.

The top of the guideway 50 between the idler roller 49 and the near edge of the upper grinding wheel I4 is closed by a hold-down bar 10 extending approximately to the axis of the lower wheel and supported by a bracket II also projecting from column II. Another hold-down bar 12 forms a continuation of bar 18, but is arranged for vertical adjustment on a support 13 dovetailed in a bracket 14 fixed on the exhaust hood 15 or casing surrounding the upper wheel I4.

This second hold-down bar 12 is therefore capable feed rollers 49 and the outer edge of the lower of careful vertical adjustment, as well as the 75 platen 62 immediately below it, for purposes that will presently appear. From the platen 62 and hold-down bar 12, the rings are projected through the grinding zone between the lapping surfaces I4 and I5 of the upper and lower grinding wheels, being guided and held against lateral displacement in this zone by the guide bars 56.

At the discharge end of theguideway59 immediately adjacent the rear edge of the lower wheel I5 is mounted a receiving platen I6 adjustably mounted on a bed plate 'II by three countersunk screws 18 and intervening rubber washers I9. The bed plate 11 is supported by a bracket 89 extending from the main column II. Similarly, a second bracket 8| supports the rear end of a hold-down plate 82 having a flared rear end portion and being vertically adjustable by means of a pair of rods 83, 83 (see Figs. 9-12)' 86 supported on and depending from the bracket 8|. In the form shown, a plurality of depending stripper fingers 81, 81 are formed integral with the rear edge ofthe hold-down plate 82, with their lower faces inclined downwardly and rearwardly, as shown in Fig. 10, to direct the finished rings 41 into the chute 96 as they are droppe oif of the receiving platen I6.

Referring now to the means for dressing the surfaces I I and I5 of grinding wheels I4 and I5 so as to maintain them at proper working distances and in proper cutting condition, reference may be had to details shown in Figs. 5, 13, 14 and 15. The dressing mechanism for both wheels is substantially identical, excepting, of course, that the dressertools for said wheels, together with their associated parts, are mounted in inverted relation to each other. Accordingly, a description of one of said dressing tools and its associated drive mechanism will suffice for an understanding of both.

Referring to the dressing mechanism for the upper wheel I4, a diamond pointed dressing tool 99 of any well known form is adjustably mounted on a dresser bar 9| which is reciprocably mounted in a plurality of opposed guide rolls 92, 92 on a supporting bracket 93. In the form shown, said supporting bracket is mounted as by bolts 93 on the outer face of the casing 29 within which the wheel I4 is rotatably mounted, and said bracket 93 overhangs the side of said wheel opposite the main column II of the machine.

The guide rollers' 92, 92 are arranged so that the bar 9| with its dresser tool 99 traverses the.

working surface I 4 of the grinding wheel in a straight line extending radially of said wheel. The cutting heightof the diamond tool 99 is adjusted in any suitable manner, as for instance by wing nut 94 on bar 9|, the adjustment being facilitated by means of a gauge stool 99* 'adjustably mounted on a support 99 fixed on the inner face of the bracket 93 within the range of traversing movement of the dresser tool 99.

The dresser bar 9| is reciprocably driven by a rack 95 thereon engaged by a pinion 96 on upright drive shaft 91. As shown in Fig. 12, the drive shaft 91' is operatively connected by chain I99 and sprockets |9I and I9I with a similar drive shaft 91 of the other dresser bar 9| associated with the lower wheel I5. The arrange-' ment issuch, that one dresser bar, as for instance bar 9|, is in its outermost position at the time that the other bar 9| is in its innermost position, and vice versa, and the two bars reciprocate in alternate directions with respect to each other. The two dresser bars are thus driven simultaneously from a common drive motor 98 and reduction gearing99 mounted on the base I9.

Reciprocating movement of the two dresser bars is effected by reversing the direction "of drive of the motor 98 through electric control mechanism which is illustrated in the diagram, Fig. 15. This diagram shows two alternativelyoperable control circuits, one of which is designed to effect reversal of themotor at the end of each stroke of the dresser tools across their respective wheel surfaces, but with a substantial time lag or period of pause at the end of each stroke. For convenience in the following description, this form of control is termed intermittent drive. The second circuit connection is designed to effect reversal of the motor at theend of each stroke without pause or time lag, which for convenience herein is termed continuous drive.

The intermittent drive circuit connections are controlled primarily from a cam member I95 suitably driven by a constant speed motor, as for instance the same drive motor 39 that is used for the compensating .feed of the upper grinding Wheel I4. The cam I95 has a fiat surface I96 thereon adapted to be successively engaged by a pair of followers I91 and I98 on opposed contact switches I99 and II9, respectively. The control circuit connections are supplied through-a switch indicated generally at III connected to the main circuit conductor II2. The switch IIIcompletes control connections for intermittent drive in one position, and for continuous drive in the other position.

The intermittent drive connectiqnsfrom main I22 of the motor-reversing switch I25, and from.

thence to the return line conductor I29. Due 'to the arrangement of the cam I95, the switches I99 or II9 will be alternately closed in timed relation, when the followers I91 and I98 pass along the flat portion I96 of said cam. The limit switches H8 and II9 are normally closed. The shaft I2 t of reversing switch I25 is normally maintained by suitable tension means such as springs I23 in an intermediate position, and the motor connections can only be completed by energizing solenoid Ill or solenoid I22 to close one of the motor circuits. As soon as the energizing circuit of one or the other of said solenoids is broken, the switch shaft I24 is automatically returned by springs I23 to its intermediate posi- 7 tion to shut off the motor; I

The operation of the intermittent control connections just described is as follows:

Assuming that the follower IN is on the flat portion I96 of cam I95 as shown in the diagram,

' a circuit will be completed through switch I99,

switch H8 and solenoid II'I. Energizing of the solenoid I I1 throws the control arm I23 of motor reversing switch. I25 in a, direction to bring a series of contactor arms I26, I21, I28 and I29 on shaft I24 into engagement with contacts I26, 7

I 21 I28 and I 29, respectively. The contactor arms I26, I21, I28 and I29 are thus directly connected, respectively, to four motor leads arranged as in well known motor design so as to drive the motor in one direction, as for instance with two leads I26 and I21 connected through conductor I30 to the main line conductor H2, and with the other two leads I28 and I29 connected through conductors I3I and I to the main line conductor I I3. Operation of the motor will be continued as long as the follower I01 remains on the flat portion I06 of cam I05, unless in the meantime the circuit is broken by the opening of limit switch IIB, under conditions as will hereinafter be described.

When cam I95 is rotated further to raise the follower I01 of switch I09, the circuit is broken, solenoid H1 is deenergized, and the motor con- I nections are automatically broken by switch I v in the reverse direction.

The two limit switches II 8 and H9 are directly responsive to the movement of said dresser bars, so as to prohibit overrun at the ends of their stroke in opposite directions. In the form shown herein, said limit switches are mounted on bracket 93* which supports dresser bar 3|, as shown in Fig. 13. The guide bar 9| has a pin I32 mounted thereon and projecting into position to engage plunger H8 or N9 of limit switches H8 and H9, respectively, and open the latter when said guide bar reaches its limits of reciprocable move-- ment. Thus the circuit through one or the other energizing solenoids H1 or I22 will be broken to stop the motor at the end of each stroke of the dresser bars, regardless of the operation of the .timing cam I05. In practice, said timing cam I05 is arranged and driven at such speed that switches I09 and H0 will be closed for at least a suflicient time to move the dresser bar the full length of its stroke, but the limit switches H8 and H9 operate automatically to prohibit overrunning of the motor in either direction.

As previously stated, the continuous drive circuit control operates to reverse the motor at the end of its stroke in both directions without any time lag or waiting period. In the arrangement illustrated inthe wiring diagram (Fig. 15), the

continuous drive circuit is connected for operation from the same power leads H2 and H3 through the switch I I I, so that the solenoids H1 and I22 of the motor reversing switch I25 are automatically operated through a two-way re- 'duction mechanism 99 (see Fig. 5).

1 known snap action type in which finger I38 operates a contact member I42 adapted to selectively close switches I40 and I4I.

When the switch III is set for continuous dressing, the power lead I I2 is connected through conductor I43 to the contact member I42, and from thence either to switch I40 or I4I, depending upon which direction the finger I38 has last been thrown by pin I31. When the contact member I42 closes switch I40, the circuit is completed through conductor I44, solenoid II1, conductor I20 and power lead II3 to start motor 98 in one direction. When the pin I31 is rotated into engagement with switch finger I38, the circuit through solenoid II 1 will be broken and anew circuit established through switch, I4 I, conductor I45 and solenoid I22 so 'as to effect reversal of the motor through the reversing switch I25.

Under most operating conditions, I find that it is usually preferable to employ intermittent dressing, with a rest period of, say, two or three minutes at the end of each stroke of the dresser bars. Due to the extremely low rate of feed of the grinding ,wheels usually employed in ma-, chines of this character, I find that the surfaces of the wheels are usually kept in better cutting condition with intermittent dressing, which permits sufiicient feed of the wheels between suc cessive strokes to give the dressing diamonds a substantial cutting effect on the abrading surfaces, whereas with continuous dressing the cuttingtool may tend to have more of a glazing or smoothing effect on the abrading surfaces. However, under certain other operating conditions continuous dressing may be satisfactory.

Means are also provided for disengaging the dresser bars and their drive shafts 81 and 9'! from the motor 98 so as to assist in various adjustments of the machine. In the form shown, the sprockets IOI and IN are fixed on their respective drive shafts, but the sprocket IN is provided with a vertically disposed drive pin I adapted to be detachably engaged in a recessed hub I5I which is directly driven from the gear re- By liftin the pin I50 out of engagement with the hub I5I', the shafts 91 and 91 are free to rotate independently of the motor. In order to assist rotation of the dresser bars manually, a hand lever I52 (see Fig. 2) is provided for detachable engagement with the upper end of drive shaft 91. This arrangement is particularly designed for adjusting the height of the dressing tools on their gauge stools.

Among the principal features of novelty of the machine constructed as above described, is the arrangement whereby the piston rings or the like are fed between the two opposed but offset grinding wheels I4 and I5 in a straight line substantially intersecting the axes of the two wheel spindles. Thus while passing between the two grinding surfaces rotating in opposite directions,

.the piston rings are progressed substantially at right angles to the mean directions of rotation of the opposed wheels so that there will be a minimum tendency toward rotation of the piston rings while passing through the grinding zone.

In carrying out this feature, it will be noted that the guideway 50 is arranged at a substantially uniform level through the machine (see Figs. '1 .and 9). The vertical dimension of said guideway 50 before the rings pass into the grinding zone is adjusted to accommodate the unfinished rings so that theypass over the free outer periphery of the lower wheel with only the slight abrasive action on the under surface of the rings due to the weight of the rings resting by gravity on the grinding surface. This initial abrasive action, however, is helpful in removing dirt and minor burrs on the bottom surface of the rings before they are fed between the wheels.

It will be observed further that the grindin wheels are urged by gravity towards the work as the studs 35 are backed off mechanically by the wear-compensating drive gearing, but that said wheels are free to move away from each other under unusual operating conditions such as the accidental introduction of rings of excessive thickness or hardness.- Operation of the machine is therefore much safer than would be the case with a positive mechanical feed for the grinding wheels.

The arrangement of the platens forming the bottom of the ring feeding guideway E and their adjustment is a further novel feature of the machine. The platen 60 at the front of lower wheel 15 is normally disposed substantially fiush with the exposed-upper surface of said wheel, so the rings can be moved directly onto the latter. From said surface the rings are progressed to platen 6|, mounted within the recessed central portion 63 of said lower wheel l5. This platen is preferably adjusted so as to be slightly below the level of the upper surface of said lower wheel, as indicated in somewhat exaggerated form in Fig. 11. The next feed platen 62 is given an even more careful adjustment in a horizontal plane at a predetermined level below the adjacent upper grinding surface of the lower wheel, which difference in level is substantially equal to the amount of material that is to be taken off of the lower-face of the piston ring in the grinding operation. In practice, I find a difference in level in the order of .0005 inch is satisfactory for this purpose. Similarly, the adjustable holddown bar 12 immediately above the platen 62 is carefully adjusted both vertically and planarly so as to be spaced approximately the same distance above the working surface of the upper disc wheel.

With the parts adjusted as above described, the piston rings are held in fairly close, vertical confinement between the platen 62 and the top bar 12 while being fed between the wheels so as to prevent tilting of the rings, or uneven grinding of their upper and lower surfaces.

The receiving platen l6 and the superimposed hold-down plate 82 are also given careful adjustment, but in this case the platen I6 is maintained at the same level as the adjacent bottom wheel l5 so that each piston ring will be discharged thereon and maintained in a horizontal plane until it has fully passed from between the wheels, as indicated in Fig. 10. i

A further advantageous feature of my improved machine is the arrangement of the grinding wheels in oflset relationship so as to facilitate the use of automatic dressing mechanism while the machine is in operation. It will be observed that the dresser bars 9|, 9& are guided for rectilinear reciprocation so as to move their respective dressing tools in a straight line extending radially of their respective disc wheels. This feature affords an. especially simple, rigid and effective mechanism that is superior to dressing mechanisms previously utilized for a similar purpose.

' Although I have shown and described one particular embodiment of my invention, it will be understood that I do not wish to be limited to the exact construction shown and described, but that various changes and modifications may be made without departing from the spirit and scope of my invention as defined in the appended claims.

I claim as my invention:

1. In a grinding machine of the class described, the combination of a base, a pair of upright spindles journalled on said base withptheir axes in offset relationship, annular grinding discs mounted in opposed relationship on said spindles, with the inner edge of each of said discs arranged substantially tangential with the outer edge of the other disc in the zone of maximum lapping of said discs, means for successively feeding a plurality of similar work pieces disposed at one side of the lower disc, and means for guidingsaid work-pieces across the open surface of said lower disc and then between the lapping faces of both of said discs, said guiding means'including a supporting platen disposed within the lower disc and another supporting platen disposed adjacent the outer edge of said lower disc opposite said feeding means.

2. In a grinding machine of the class described, the combination of a base, a pair of upright spindles journalled on said base with their axes in offset relationship, annular grinding discs mounted in opposed relationship on said spindles,

with the inner edge of each of said discs arranged substantially tangential with the outer edge of the other disc in the zone of maximum lapping of said discs, and means for feeding and guiding a plurality of similar work pieces between the lapping faces of said discs, said feeding and. guiding means including a platen disposed within and below the level of the lower disc, and another platen disposed adjacent the outeredge of said lower disc and substantially in the same plane thereof and adjustable supporting means for each of said platens comprising a bracket rigid with the base, a plurality of threaded members connecting said bracket with said platen at a plurality of horizontally spaced points, and compressible elastic supporting material interposed between said bracket and said platen adjacent said threaded means.

3. In a. grinding machine of the class described, the combination of a base, a pair of spindles journalled on said base with their axes in offset relationship, annular; grinding discs mounted in opposed relationship on said spindles, with the inner edge of each of said discs arranged substantially tangential with the outer edge of the other disc in the zone of maximum lapping of saiddiscs, and means for feeding and guiding a plurality of similar work pieces between the lapping faces of said discs in a direction extending generally along the radial line common to both disc's, said feeding and guiding means including a pair of spaced metal bands extending between the lapped surfaces of said discs and having adjustable anchoring means at opposite ends thereof for maintaining them under'tension.

RALPH wanna round. 

